(c) 2/3
From the question it is given that,
4/5 of 5 kg apples were used on Monday = (4/5) × 5
= 20/5
= 4 kg
Then,
The next day 1/3 of what was left was used = (1/3) × 1
= 1/3 kg
So, Weight (in kg) of apples left now is = 1 – (1/3)
= (3 – 1)/3
= 2/3 kg of apples